The campaign against Scottish independence must move beyond economics to arguments of the "head and heart", Prime Minister David Cameron has said.

The UK offers security in a "diverse, dangerous world", according to Mr Cameron, who said he will "work very hard to play my part" in the referendum.

However, Number 10 has confirmed that the Prime Minister will not take part in a public debate with Scottish First Minister Alex Salmond, following a new SNP poll indicating a substantial proportion of the British people would like to see them go head-to-head on television.

Speaking in the Sunday Times Scotland newspaper, Mr Cameron said: "We've just got to keep pushing both the arguments of the head and those of the heart.

"I think the arguments of the head we've been winning very strongly. We now need to win some of the arguments of the heart.

"The UK is not something to want to belong to simply for economic reasons, but actually for emotional and historic reasons."

He added: "In a diverse, dangerous world, the security of the United Kingdom; the ability to be part of something that could be a great success story, just as it has been in the past - we need to win those arguments."

He continued: "Obviously I'm very concerned that we win this referendum. I think the argument has been going the way of the United Kingdom, but it will not be won until every last vote is counted.

"I'll work very hard to play my part."

Mr Cameron has come under renewed pressure for a televised debate with Mr Salmond following his New Year message urging England, Wales and Northern Ireland to send a message to Scotland that "we want you to stay".

Mr Cameron has steadfastly refused Mr Salmond's challenge, insisting the debate should be amongst the people of Scotland.

But in a new letter to Number 10, Mr Salmond told the Prime Minister that his New Year plea to Scotland undermined this argument.

Mr Salmond said: "I note that you used the centre-piece of your New Year address to attack Scottish independence.

"It seems that you want to dictate the terms of the debate about Scotland's future without taking the democratic responsibility to defend your views in open debate. That is simply unacceptable."

A Number 10 spokeswoman said: "The Prime Minister is Prime Minister of the whole United Kingdom and of course has a role in the referendum campaign, however, he believes that the debate should be led by Scots in Scotland and that is why Alistair Darling will lead for the No campaign."

A Panelbase poll, commissioned by the SNP, found over three-fifths of people in Scotland and over half in the rest of the UK want a TV debate between Mr Salmond and Mr Cameron, compared with around a quarter on both sides of the border who do not.

Deputy First Minister Nicola Sturgeon said: "While David Cameron is happy to pull the strings of the No campaign from 10 Downing Street, he is scared to debate with Alex Salmond face-to-face.

"As the principal signatories of the Edinburgh Agreement, the natural progression in these circumstances is a televised, head-to-head debate between Mr Cameron and Alex Salmond - a democratic position supported by a substantial majority of people north and south of the border."

A spokesman for pro-independence campaign Yes Scotland said: "A televised debate with the First Minister and Prime Minister will help Scots choose between the two futures on offer and ensure that the UK Government fully explains why it is willing to implement unwanted policies north of the border."

"On the issue of the debate, I know why Alex Salmond is pushing this argument - it's because he's losing the current argument and he wants to try and change the argument," he said.

"But this is not a debate between me and him. The debate should be between people in Scotland who want to stay and people in Scotland who want to go."

Mr Cameron agreed that the referendum decision will affect everyone in the UK, but insisted the debate should take place in Scotland.

He added: "We debate these things in parliament and we debate them in the media.

"But the key question - does Scotland stay in the UK or does Scotland leave the UK? - that is for Scots to decide.

"I don't have a vote in this. It is for Scots to decide and that is where the debate should take place."

Mr Salmond described Mr Cameron's position on a TV debate as "increasingly ridiculous", and insisted that the Prime Minister will be "dragged into the television studio" eventually.

"David Cameron's attitude is the same mix of arrogance and fear that saw the Tories seek invisible cuts to Scotland's budget in the 1980s and plan £4 billion of cuts for the future," he said.

"Arrogance because his government wants to dictate the terms of the debate but refuses to take part in a public debate and fear because he knows, as people across Scotland do, that he represents a government Scotland did not elect.

"The Prime Minister's position is increasingly ridiculous. He cannot on the one hand tell the BBC that the referendum debate will take place in the media and then simply refuse to debate.

"A majority of people, not just in Scotland but in the rest of the UK, think it is right that the Prime Minister takes part in a debate and I would suggest David Cameron listens to them.

"He can only hide from this for so long. Eventually he is going to be dragged into the television studio and have the democratic responsibility of an open, free debate."